Field of the Invention
The present invention relates to alpha-amylase variants, polynucleotides encoding the variants, methods of producing the variants, and methods of using the variants.
Description of the Related Art
Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 3.2.1.1) constitute a group of enzymes, which catalyses hydrolysis of starch and other linear and branched 1,4-gluosidic oligo- and polysaccharides.
There is a long history of industrial use of alpha-amylases in several known applications such as detergent, baking, brewing, starch liquefaction and saccharification e.g. in preparation of high fructose syrups or as part of ethanol production from starch. These and other applications of alpha-amylases are known and utilize alpha-amylases derived from microorganisms, in particular bacterial alpha-amylases.
Among the first bacterial alpha-amylases to be used were an alpha-amylase from B. licheniformis, also known as Termamyl which have been extensively characterized and the crystal structure has been determined for this enzyme. Bacillus amylases, such as Termamyl and SP707, form a particular group of alpha-amylases that have found use in detergents. Many of these known bacterial amylases have been modified in order to improve their functionality in a particular application.
Methods of increasing the thermostability of alpha-amylases have been well studied. Suzuki et al. (1989) disclose chimeric alpha-amylases, in which specified regions of a B. amyloliquefaciens alpha-amylase have been substituted for the corresponding regions of a B. licheniformis alpha-amylase. The chimeric alpha-amylases were constructed with the purpose of identifying regions responsible for thermostability. Such regions were found to include amino acid residues 177-186 and amino acid residues 255-270 of the B. amyloliquefaciens alpha-amylase. Igarashi et al. 1998 show that the thermostability of AmyS-type amylases can be increased by the deletion of two amino acid residues, R179-G180, (AmyS numbering) from a loop (F178 to A184). However, Shiau et al. (2003) showed that an AmyS enzyme with deletion in the same loop has a lower specific activity for corn starch hydrolysis at high-temperature than the parent enzyme, negating one of the principal advantages of AmyS amylases.
For environmental reasons it has been increasingly important to lower the temperature in washing, dishwashing and/or cleaning processes. However, most enzymes including amylases have a temperature optimum which is above the temperature usually used in low temperature washing. Alpha-amylase is a key enzyme for use in detergent compositions and its use has become increasingly important for removal of starchy stains during laundry washing or dishwashing. Therefore, it is important to find alpha-amylase variants, which retain their wash performance, stain removal effect and/or activity when the temperature is lowered. However, despite the efficiency of current detergents enzyme compositions, there are many stains that are difficult to completely remove. These problems are compounded by the increased use of low (e.g., cold water) wash temperatures and shorter washing cycles. Thus, it is desirable to have amylolytic enzymes that can function under low temperature and at the same time preserve or increase other desirable properties such as specific activity (amylolytic activity), stability and/or wash performance.
Thus, it is an object of the present invention to provide alpha-amylases variants which have high performance, in particular high wash performance, at low temperatures and/or which have high stability in detergent compositions and/or which have high amylase activity after storage in detergents.
It is another object of the present invention to provide alpha-amylase variants that exhibit a high level of stability when incorporated into detergent compositions such as liquid detergents, in particular in the presence of chelating agents, surfactants, proteases and/or alkaline conditions.
The present invention provides alpha-amylase variants with improved stability compared to its parent.